A. Field of the Invention
This invention relates to an automatic drive pulley, more specifically to an improved drive pulley capable of having a wide variation in effective pulley radius and automatically performing predetermined mechanical control functions.
B. Description of the Prior Art
In the selection of a drive pulley, it is common practice to determine the effective pulley radius and the dimensions of the pulley working surface to closely match the power of the energy source with the power requirement of the load. In cases where the torque requirement of the load varies significantly, means must be provided to avoid a significant mismatch between the power of the energy source and the power requirement of the load.
Prior art inventors have created mechanisms to minimize or avoid such a power mismatch. Prior art mechanisms are those that require manual intervention and those that automatically sense load and self adjust the effective pulley radius in the desired direction.
Prior art mechanisms requiring manual intervention include the stepped pulley, the conical pulley, the stepped sprocket and the manually adjustable split pulley.
Among the earliest to develop drive pulleys with automatic load-sensing and self-adjusting features is John C. Pratt. Pratt's pulleys under U.S. Pat. No. 616,630 issued December 1898 and U. S. Pat. No. 663,928 issued December 1900 self adjust to an increase in load by reducing the radius of the drive pulley. With a decrease in load, Pratt's pulleys adjust in the opposite direction. Pratt uses coil springs to create the automatic effect and rigid linkages to connect the sheave segments to the shaft.
U.S. Pat. No. 4,652,250 issued March 1987 and U.S. Pat. No. 4,741,546 issued May 1988 to James B. Reswick, U.S. Pat. No. 4,373,926 issued February 1983 to Robert L. Fullerton, U.S. Pat. No. 3,969,948 issued July 1976 to Charles A. Pipenhagen, Jr. and U.S. Pat. No. 4,836,046 issued June 1989 to Gilmore H. Chappel disclose automatic transmisions with load-sensing and self-adjusting features. The drive pulley of the transmissions use torsion springs to create the automatic effect and rigid linkages to connect the sheave segments to the shaft.
U.S. Pat. No. 5,407,395 issued April 1995 to Hubert Kramer discloses a steplessly variable belt drive for bicycle with load-sensing and self-adjusting features. The drive pulley of the transmission uses rigid arms as sheave segments and pivoted at the hub. Compression springs are used to urge the rigid arms outward and to create the automatic effect.
The use of rigid linkages or rigid arms in the above-mentioned prior art devices limits the variation in effective pulley radius due to mechanical interference.
U.S. Pat. No. 4,342,559 issued August 1982 to Robert N. Williams discloses a drive system with load-sensing and self-adjusting features. The drive system uses two sideplates to position the sheave segments. The drive pulley of the drive system uses helical tension springs or a horseshoe spring to create the automatic effect.
Prior art mechanisms in the field of automatic drive pulleys provide a rough adjustment of the drive pulley radius in the desired direction to minimize the mismatch between the power of the energy source and the power requirement of the load. They all adjust within the pulley operating range such that an increase in belt tension is followed by a decrease in effective drive pulley radius and vice versa. However, the relationship between the belt tension, input torque and effective drive pulley radius in the pulley operating range is not well defined. There is no prior art for automatic drive pulleys that can be customized to perform a predetermined automatic control function over the pulley operating range.